1. Field of the Invention
The present invention relates generally to an optical apparatus for use with a light-providing optical system of a liquid-crystal projector; and more particularly to such an optical apparatus which can be miniaturized.
2. Description of the Related Art
Projection type display apparatus which can generate large-sized pictures by projecting images onto a screen on an enlarged scale have heretofore been widely spread. These large-screen image display apparatus may be used both indoors and outdoors. These projection type display apparatus are roughly classified into two categories. First, a projection type display apparatus (CRT projector) projects light from a fluorescent screen of a CRT onto a screen. Second, light from a light source is modulated by a spatial light modulator element and thereby projected onto a screen. In the latter type of projection type display apparatus, a liquid-crystal panel is typically used as the spatial light modulator.
FIG. 7 shows an example of an arrangement of a conventional single-panel transmission type liquid-crystal projector. Light (white natural light) is emitted from a light source 31 and is projected incident on a lighting optical system 41 which introduces this emitted light into a liquid-crystal panel 51. As seen from the side of the light source 31, lighting optical system 41 includes a MLA (multi-lens array) 42, a MLA 43 and a condenser lens 44.
MLA array 42 comprises a plurality of small (e.g., typically approximately 1 to 15 mm in diameter) lenses 42a arranged in a two-dimensional array-type fashion as shown in FIG. 8. The shape of lens surface of each lens 42a is rectangular, and is dimensioned to be substantially similar to the aspect ratio of the panel surface of liquid-crystal panel 51. A peripheral portion of light emitted from light source 31 is projected incident on one or more lenses 42a at a peripheral portion of MLA 42. A central portion of light emitted from light source 31 is projected incident on one or more lenses 42a at a central portion of MLA array 42.
MLA 43 is disposed at substantially the focal point position of lenses 42a of MLA 42. MLA 43 comprises a plurality of small lenses 43a arrayed in a two-dimensional fashion in a one-to-one relation to lenses 42a of MLA 42. Light emitted from each respective lens 42a of MLA array 42 is projected respectively incident on the corresponding lens 43a of MLA 43. The combination of MLA 42 and MLA 43 may be referred to as a light integrator.
Light emitted from each lens 43a of MLA 43 is projected incident on condenser lens 44. An optical path length from condenser lens 44 to liquid-crystal panel 51 is substantially equal to a focal length f of condenser lens 44. Light focused by condenser lens 44 is therefore projected incident on the panel surface of the liquid-crystal panel 51.
Multi-lens arrays 42, 43 and condenser lens 44 function to superimpose a central portion and a peripheral portion of light emitted from light source 31 so that light having uniform intensity is projected incident on the entire panel surface of liquid-crystal panel 51.
Liquid-crystal panel 51 is a transmission type liquid-crystal panel employing a TN (twist nematic) liquid-crystal. Incident light that is linearly polarized in one vibration direction passes a polarizing plate (polarizer) on the surface of the incident side of liquid-crystal panel 51 and advances to a liquid-crystal layer. When this linearly polarized light passes through the liquid-crystal layer, the polarizing axis is rotated in response to a voltage level applied to the liquid-crystal layer. The linearly polarized light is passed through an RGB color filter and is detected by a polarizing plate (polarizer) at a surface of an emitting side of liquid-crystal panel 51. Thereafter, light that passes through liquid-crystal panel 51 is projected onto a screen (not shown) through a projection optical system 61.